The present invention relates to flat panel displays, particularly to flat panel displays using liquid-crystal materials, and more particularly to pixel elements for flat panels displays utilizing active matrix pixel circuits, mematic curvilinear aligned phase films, and counter electrodes laminated together, and method of fabricating such pixel elements.
Conventional processing techniques used to fabricate active matrix liquid crystal displays (AMLCDs) require processing temperatures of at least 300.degree.-350.degree. C. Temperatures in this range are too high for most plastic substrates, and presently all AMLCDs are fabricated on substrates made of silicon, quartz, or glass. These substrates are inherently brittle and often break, providing the most common failure mechanism seen for portable electronic systems.
Recently a very low temperature (.ltoreq.100.degree. C.) process has been developed to fabricate active matrix pixel circuits on plastic substrates, as described and claimed in copending U.S. application Ser. No. 08/940,104, filed Sep. 29, 1997, entitled "Display Pixels Driven By Silicon Thin Film Transistors And Method Of Fabrication".
Polymeric liquid crystal material, such as nematic curvilinear aligned phase (NCAP) films developed by Raychem Corporation, also known as polymer dispersed liquid crystal (PDLC), are particularly amenable to large-area displays with plastic substrates and have been marketed commercially for years in such applications. Because the NCAP emulsion can be coated directly onto a continuous plastic web and the water dried off to form a uniform film it has been found that the NCAP material itself may provide a uniform spacing between electrodes, with no spacer beads or cell filling necessary.
A major hurdle for applications of the NCAP films to date has been the necessity to drive each pixel directly. The electro-optical response curve of transmission versus voltage is not sufficiently steep for NCAP materials to allow use of the same sort of multiplexing schemes possible for twisted nematic (TN) or supertwisted nematic (STN) displays. Furthermore, the NCAP materials are not typically bistable, which can allow other means of multiplexing.
The present invention combines the silicon thin-film transistor (Si-TFT) on plastic based pixel fabrication, of the above-referenced copending application, with Raychem Corporation's NCAP polymeric liquid crystal material to fabricate lightweight, rugged, and flexible pixel elements for AMLCDs.